1. Field of the Invention
The present invention relates to an image processing apparatus and image processing method for controlling the total amount of toner or ink in print processing, and a computer-readable medium storing a program for generating image processing parameters.
2. Description of the Related Art
A color printer which uses a printing material (color material) such as toner or ink often has a limit in the amount of a printing material that can be used for each pixel. For example, an electrophotographic printer which uses cyan/magenta/yellow/black (to be referred to as C, M, Y, and K, respectively, hereinafter) toners will be examined. In this electrophotographic printer, when the maximum value of a toner output of each color for each pixel is 100%, the limit value of the total amount of toner for each pixel is defined as, for example, 300%. If the total amount of toner exceeds 300%, a failure in toner fixing or toner scattering may occur, resulting not only in degradation of the image quality but also in damage to the apparatus main body.
To solve the above-mentioned problem, the total amount of C, M, Y, and K toners is calculated for each pixel, and the total amount is decreased if it exceeds a limit value (see, for example, Japanese Patent Laid-Open No. 2007-334320). Processing of controlling and outputting the total amount of toner will be referred to as “toner total amount control processing” for convenience. In Japanese Patent Laid-Open No. 2007-334320, K toner is increased while decreasing C, M, and Y toners by equal amounts. Accordingly, the total amount of toner can be decreased while minimizing a change in image quality. When limiting the total amount of toner, an LUT (Look Up Table) or the like can be used to convert a density value into information on the amount of consumed toner, implementing accurate toner total amount control processing.
However, the conventional technique of controlling the total amount of toner has a problem in that a signal distorts before and after toner total amount control processing occurs. Although details will be described later, conventional toner total amount control processing is performed after temporarily converting a density value into information on the amount of consumed toner using an LUT or the like. Then, the toner amount information after toner total amount control processing is converted back into a density value using an LUT or the like. At this time, the relationship between the density value and the amount of consumed toner is not always linear. For example, an amount of toner consumed when the density value is 100% may be more than double an amount of toner consumed when the density value is 50%. That is, the relationship between the density value and the amount of consumed toner may become non-linear.
Hence, information is lost in the process of converting a density value into an amount of consumed toner and the process of converting an amount of consumed toner into a density value because compression of a value and the like are done with a non-linear relationship. Since these processes are executed for all pixels, the gradation characteristic of an image and the like degrade due to loss of information, resulting in poor image quality.